The present invention relates generally to candle wicks and methods of making the same. More specifically, the present invention relates to candle wicks of knit construction which may be satisfactorily used in candles due to their high yield combined with improved capillary flow and increased functional surface area. In addition, the present invention enhances product safety by providing an improved self-trimming wick capable of maintaining a substantially uniform and stable wax pool and burn rate.
Candles employing a wick have been in existence for many centuries. A typical candle has a single wick, or multitude of wicks, that extends longitudinally through the body of the candle. Single wicks are usually centrally disposed in the candle body. The combustible candle body is typically a thermoplastic blend of petroleum (paraffin) wax, mineral (montan) wax, synthetic wax (polyethylene or Fischer Tropsch) or natural waxes (vegetable or animal). Clear candle waxes, known as gel candles, have gained recent popularity due to there diverse decorating potential. These gel candles are made from mineral oil and special resins. Natural, plant based soybean wax is gaining popularity as a cost competitive, environmental or xe2x80x9cgreenxe2x80x9d wax derived from renewable resources. Various additives used to modify the candle hardness, color, burn rate and aroma are well know in the trade and include, for example, stearic acid, UV inhibitors, polyethylene, scent oils and color pigments.
Upon lighting a candle wick, the heat melts the wax which then travels up the wick by capillary action and is vaporized. Performance requirements of a wick in a candle include the ability to create and maintain the desired burn rate, the ability to create and maintain the desired wax pool and, if specified or required, the ability to bend or curl to maintain the proper wick height (referred to in the trade as xe2x80x9cself-trimmingxe2x80x9d). In addition to these performance requirements, it is important that the finished wick be stable and not subject to size fluctuation when tension is applied to the wick during the candle making or wick pre-waxing process. The ability of the wick to be self-supporting may be preferred, or even required, in certain candle types or candle manufacturing processes.
Burn rate and flame height is influenced by the capillary flow rate, capillary flow volume and/or functional surface area of the wick. Capillary flow rate or the rate of fuel delivery is controlled by the size of capillaries available in a given wick. The size of capillaries is the distance between materials that are creating capillaries. The material that creates capillaries is the individual fibers or filaments within a wick. The distance between, or force applied to, these fibers or filaments determines the size of the capillaries. Therefore, the size of the capillaries is primarily dependent upon the stitch/pick tightness or density of the wick. It is known in the trade that increasing wick density or stitch tightness will reduce the flame height or burn rate. This is due to the fact that tighter stitches reduce the size of the capillaries, thereby restricting or reducing the capillary flow rate. Conversely, reducing the wick density or stitch tightness will increase the flame height or burn rate by increasing the size of the capillaries thereby increasing the capillary flow rate. Capillary flow volume is controlled by the number of capillaries within a wick. The number of capillaries is the amount of surface area within a wick that provides for capillary action. Given the same wick size and density, fiber or filament size controls the number of capillaries or surface area available for capillary action. Thus, the smaller the fiber or filament diameter within a wick, the more capillaries and the greater the capillary flow volume and vice versa.
Functional surface area is the amount of the surface area exposed to temperatures which are sufficiently high to cause vaporization. Wick size (diameter or width) as well as surface contour, will influence the functional surface area of the wick. For example, assuming a constant capillary flow rate, increasing the wick width or diameter will increase not only the capillary flow volume but also the functional surface area and thus increase the flame height or burn rate. Furthermore, the same size and density wick with an undulated exterior surface (i.e., a surface having distinct peaks and valleys) will exhibit a greater functional surface area and, assuming a sufficient capillary flow rate, will produce a higher burn rate and flame height as compared to the same wick with a relatively smooth exterior surface contour.
The ability of the wick to bend or curl is typically preferred and in certain candle types (i.e. tapered or stick) may even be required. The wick curl causes the end of the wick to lean out to the lateral edge of the flame where higher temperatures burn it away. As a result of the wick burning at its terminal end, it becomes self-trimming. Without a self-trimming feature, a wick will quickly become too long, producing a large flame that emits excessive soot while burning as well as producing a large carbon head at the tip of the wick. Wicks that do not curl must be trimmed frequently to maintain the proper flame height or burn rate and wax pool diameter. Conversely, it is important that a wick does not over-curl or bend to the point were the terminal end touches the wax pool. This will either extinguish the candle or cause an excessive flame height and burn rate. In addition, it is important that the wick, once it bends to the outside of the flame, does not continue to curl and create a spiral curl. A wick that curls to, and remains at, the outside edge of the flame and thus becomes self-trimming is typically preferred and in certain candles may even be required for proper, safe performance.
The wick must also create the desired wax pool. The size of the wax pool is related to the flame height or burn rate. The smaller the flame height or burn rate the smaller the wax pool. Conversely, the larger the flame height or burn rate the larger the wax pool. If the wax pool is too small for the candle, the candle will develop a tunnel down the middle of the wick as the heat from the flame is not able to melt the wax at the outer portion of the candle. If the wax pool is too large for the candle, the wax will run excessively over the edges of the candle. In addition, with regard to self-trimming wicks (i.e. wicks whose terminal end curls to the outside of the flame), the wax pool should obtain a desired maximum diameter and then maintain the desired maximum diameter as the candle burns (i.e. so as to create a stable wax pool). Equally important as self-trimming wicks achieving a stable wax pool, certain candles will require a uniform diameter wax pool. If the wax pool created by the heat of the flame is uneven or oblong in shape, the candle may burn down unevenly and in many instances will cause the melted wax to drip or run-off one side of the candle.
It is important that the finished wick material be stable so that its consistency does not change during the candle making or wick waxing process. The finished wick most preferably should have minimal stretch under load. If the wick diameter changes significantly under load (i.e. has excessive stretch or elongation), then the size of the capillaries as well as the functional surface area will change depending on the amount of tension applied to the wick during the candle making or wick waxing process. Generally speaking, the tighter the stitches the more dense the wick and thus the less stretch or more stable the finished wick. However, as noted above, the more dense a given wick is made, the smaller the capillaries and thus the lower the burn rate. It is important for wicks to be designed and manufactured with minimal stretch (i.e. high stability and consistency) while taking care not to create such small capillaries such that the burn rate is inadequate for the candle design. A wick structure or design that maximizes the size of the capillaries yet remains stable during the candle making or wick waxing process is desired.
Certain candles and/or candle making processes may require that the wick be self-supporting during the manufacturing and/or burning process. For example, a self-supporting wick is typically required when manufacturing container candles. Thus, during the manufacture of container candles, the wick is usually tabbed and placed in the bottom of the container with the top of the wick placed in a centering device at the top of the container. Such a wick must be self-supporting when the melted wax is poured into the container. If the wick is not self-supporting, it will fall over or bend when the melted wax is poured into the container. Furthermore, certain candles develop large and deep wax pools when burning. As such, the wick most preferably is self-supporting so as to prevent the wick from falling into the melted wax pool.
Candle wicks have been braided for well over the last century. Such conventional wicks are braided from multiple fiber or filamentary yarns. The most commonly used yarn is cotton although other natural fibers such as rayon have also been employed. Braiding is the intertwining of three or more strands to make a cord or narrow textile band. The strands form a regular diagonal pattern down the length of the cord. The interlaced yarns run diagonally to the production axis of the material. Braided wicks are produced in various sizes, shapes and constructions to achieve the necessary performance (flame height, wax pool size, self-trimming) and process (stability, self-supporting) requirements. Historically, wick manufacturers have offered two groups of braided wicks. One group is self-trimming wicks (i.e. wicks that curl or bend to the outside of the flame) and the other group is self-supporting wicks. Self-trimming braided wicks typically have a flat profile and may be treated with flame retardants to assist wick curl and/or minimize after-glow. Self-supporting braided wicks (also known as xe2x80x9ccored wicksxe2x80x9d) are typically round in profile and have either a paper, cotton or wire material in the core of the braid. This core material in the braided construction creates a self-supporting wick as described above.
As will be evident from the following discussion, there is a need among candle manufacturers for candle wicks capable of overcoming the limitations of conventional braided candle wicks. These performance and process limitations of the braided construction, as outlined below, are know by those skilled in the art of candle making.
One such performance limitation is that braided wick structures do not provide enough capillary flow to optimize the performance in many of today""s candles. Specifically, an improved wick is needed for the higher viscose natural waxes such as vegetable or soybean waxes as well as the newer gel waxes. When manufacturing a braided wick, it is well known by those skilled in the trade that increasing the picks per inch will increase the density of the wick (i.e. reduce the yield) and thereby reduce the size of capillaries, thus reducing the potential flame height or burn rate. Conversely, reducing the picks per inch will open the braid and reduce the density of the wick (i.e. increase the yield) and thereby increase the size of capillaries, thus optimizing the flame height or burn rate. However, such an increase in yield and burn rate from conventional braided candle wicks is limited by the fact that creating a more open structure with large capillaries creates a less stable wick which will change in characteristics when subjected to the tensions of the candle manufacturing or wick pre-waxing process. In addition, the smooth surface of a braid reduces the functional surface area. The small capillaries and smooth functional surface area of the braided wick make it more difficult to create the required capillary flow rate in today""s natural and gel waxes as well as candles that have high amounts of additives (i.e. scents, dyes) that tend to impede capillary flow.
A further limitation of braided wick technology relates to the uniformity of the wax pool diameter. For example, conventional self-trimming braided wicks will produce an oblong wax pool. The oblong wax pool is the result of the wick curling in one direction and maintaining this fixed directional curl. The fixed directional curl causes the flame to lean in the direction of the flame, thus causing the wax pool to become permanently oblong in shape. This creates a problem in candles where the candle diameter is less than, or substantially equal to, the potential pool diameter (i.e. taper or stick candles), causing the candle to burn down unevenly and allowing the wax to drip or run-off one side of the candle.
It is also known by those skilled in the art of candle making that flat braided, self-trimming wicks may curl to the point where the terminal end bends into the wax pool or continues to curl into a pigtail shape (i.e. a spiral curl). This undesirable result can cause a self-trimming braided wick to increase in length so as to increase the amount of wick material, or functional surface area, above the melted wax pool. This in turn produces, over the length of a burn, a continually increasing (i.e. unstable) flame height and wax pool.
In summary, a higher yield, stable wick construction that improves the capillary flow and functional surface area would offer performance benefits desired by today""s candle makers. In addition, the ability of a self-trimming wick to provide a more stable and uniform diameter wax pool as the candle burns would improve candle safety.
Broadly, the present invention is embodied in knit candle wicks. In especially preferred forms, the present invention is embodied in knit candle wicks that provide a higher yield, improved capillary flow as well as an increase in the functional surface area. In addition, the self-trimming wicks of this invention are capable of creating a more stable and uniform wax pool diameter. Most preferably the knit wicks of this invention are a warp knit construction in which the interlocking loops run lengthwise in the direction of the material. In addition, the various warp knit constructions of this invention comprise both interlocking loop or warp ends as well as weft or laid-in yarns typically referred to as warp knitting with weft insertion. The present invention thus advantageously provides for a high yield, stable wick construction that improves candle safety and performance.
These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.